Nitrocellulose compositions and method for making same



portions of the cured grain.

Patented Jan. 3, 1961 NITROCELLULOSE COMPOSITIONS AND METHOD FOR MAKING SAME Lester L. Weil, Alexandria, Va., assignor to Atlantic Researc Corporation, Alexandria, Va., a corporation This invention relates to new and improved compositions comprising nitrocellulose and plasticizers and processes for making same.

This application is a continuation-in-part of application Serial Number 256,399, filed November 14, 1951, now abandoned.

The use of plasticized nitrocellulose in the production of films, coatings and molded objects of various kinds, including propellant grains, has hitherto posed a number of difliculties. To make films or coat-ings, for example, it has been necessary to dissolve the nitrocellulose and plasticizer in a volatile solvent or to suspend the plasticized nitrocellulose in water in order to form a sufficiently fluid mix for the desired application. After formation of the film or coating the volatile solvent or water must be removed. These procedures possess the disadvantages of slow drying and setting of the film or coating, costly expenditure of volatile solvents, limitation to the production only of thin films because of the necessity for solvent or water removal and shrinkage of the film or coating which in many cases is undesirable.

Where a volatile solvent or water cannot be used as, for example, in the manufacture of films of substantial thickness or molded objects of appreciable size, it has generally been the practice to mix the nitrocellulose with the plasticizer in a kneader or masticating mill to form a stilt paste or dough and then to extrude it under heat and pressure into the desired shape or to introduce the paste into a mold and subject the material to high temperatures and pressures. Such a procedure is dangerous because of the auto-oxidant properties of the nitrocellulose and is especially so when combined with such highly active materials as nitroglycerine. To minimize the hazards, an alternative method has been in use for the manufacture of nitrocellulose propellant grains.

This alternative method involves plasticizing cylindrical nitrocellulose powder directly in the mold with a nitroglycerine casting solvent. Cylindrical powders cannot be dispersed in the solvent to form homogeneous, pourable slurries except with excessively high proportions of solvent. However, since even these high fluid content slurries are unstable, the powder rapidly sediments in the casting molds. As a result, it has been necessary to employ a casting procedure which consists of filling a suitable mold with and then admitting the casting solvent into the mold from the bottom. When the casting solvent has penetrated to the top of the mold, the mold is heated until the nitrocellulose dissolves in the nitroglycerine, with resulting gelation and setting of the mixture.

This technique possesses certain serious disadvantages. The nitrocellulose tends to pack at the bottom of the mold, thus forcing the casting solvent upwards. As a result, the propellant grainis non-uniform in composition with excessive proportions of nitrocellulose relative to casting solvent at the bottom and excessive amounts of nitroglycerine at the top. In practice, this has often necessitated the wasteful removal of the upper and lower Processing difficulties are frequently caused by plugging before the mold is completely filled with the casting solvent. This plugging action is caused by solution of some of the nitrocellulose in the cylindrical nitrocellulose powder above about 10 mils the rising solvent with consequent gelation which slows up progress of the solvent and often becomes so pro nounced that the solvent cannot penetrate to the top of the mold. Plugging is encountered especially frequently in the making of long grains. To counteract this difficulty, it has been the practice to employ nitrocellulose of large particle size, since the larger the particles the slower is the rate of solution and the larger are the interstices between the particles.

The necessity for employing large size particles prevents the intimate and homogeneous distribution of a nely divided solid additive and has, therefore, made it impossible to incorporate into the grain solid oxidizers which are insoluble in the casting solvent. This disadvantage limits the use of organic casting solvents which for combustion require the presence of external oxidizers. Unless such an inert solvent is burned, the efficiency of the propellant is materially reduced.

The object of this invention is to provide homogeneous, fluid, pourable slurries of nitrocellulose in plasticizer which can be formed into films or coatings of substantially any desired thickness or molded into objects of any desired shape or size without requiring the removal of volatile solvent or other dispersion media or the application of high temperatures and pressures for molding.

Another object is to provide stable, pourable fluid slurries of nitrocellulose in a casting solvent which are substantially stable and homogeneous in character and which may be poured into a suitable mold of any desired shape or size to form propellant grains of substantially uniform composition throughout.

Still another object is to provide a process for making nitrocellulose propellant grains which permits the intimate and homogeneous incorporation of finely divided, insoluble, solid oxidizers, and the use of any suitable organic casting solvent including inert solvents which require external oxidizers for combustion.

Other objects and advantages will become apparent from the following detailed description.

I have discovered that nitrocellulose can be dispersed or suspended in a plasticizer to form a fluid slurry which is pourable, homogeneous and stable when the nitrocellulose particles are spherical and of sufiiciently small size. These fiuid slurries are readily applied as films or coatings of any desired thickness or poured into molds of any desired shape or size. They are stable, namely do not exhibit any appreciable separation or sedimentation during the curing period, and, because of the fine particle size of the nitrocellulose, are cured more rapidly than has generally hitherto been possible to form films, coatings or other molded objects which are of uniform com-- position throughout.

As aforementioned, to obtain a stable, dispersion of the nitrocellulose in plasticizer, the particles. must be spherical. This characteristic contributes both to: fluidity of the mix and makes possible the incorporation of adequate amounts of the nitrocellulose into the plasticizer without loss of fluidity. The sphericity of the particles permits them to move freely relativey to each other and thus eliminates the matting and interlocking which, in the case of cylindrical or other irregularly shaped particles, reduces fluidity and causes sedimentation. Sphericity, furthermore, makes possibe the introduction of a maximum volume of the nitrocellulose with a minimum surface area. The reduced surface area minimizes premature solvation of the nitrocellulose by the plasticizer and thus is an additional factor in promoting fluidity.

The nitrocellulose should consist, predominantly by weight, of spherical particles which are preferably not in diameter. My process will tol homogeneous:

3: erate a small proportion by number of larger particles without appreciable sedimentation. Where the smaller particles comprise a major proportion by weight, the proportion by number of small particles to particl'es'above the preferred range of size is considerably greater. When larger particle sizes predominate, the sedimentation rate is so rapid that the grains lack the necessary homogeneity.

Where it is desired to produce slurries which are not only sufficiently stable after formation to permit molding and curing without sedimentaiton but which also permit storage for a substantial period of time without loss of stability, it is desirable to employ particles which are even smaller than mils. To produce slurries which possess a shelf life as long as several days or even weeks, it is desirable to employ particles no larger than about 100 microns in diameter and preferably having a maximum average particle size of about 50' microns. In other words, the size distribution of the particles is such that the maximum average diameter by number is about 50 microns.

The desired shelf life of the nitrocellulose-plasticizer slurry is, of course, largely determined by the use to which it is to be put. Where the slurry is to be employed soon after formation, as is frequently the case in the production of propellant grains, prolonged shelf life is of relatively little importance, it being necessary only that the dispersion remain stable through the pouring and curing period. 'In many cases, however, shelf life is important, as where there is a considerable hiatus between slurry formation and use, and in such cases it is desirable to employ smaller particles within the permissible size range.

The plasticizer or casting solvent, as the plasticizer is frequently termed in the art, may be any suitable highboiling organic solvent which dissolves nitrocellulose slowly at ordinary temperatures and rapidly at elevated temperatures to form a solid gel. The solvent may be highly active, such as nitroglycerine, or substantially inert, namely non-auto-oxidant. Examples of suitable inert, organic casting solvents include triacetin, the various phthal ates such as diethyl phthalate, dibutyl phthalate, dioctyl phthalate, di-(methoxyethyl) phthalate, methyl phthalyl ethyl glycolate, ethyl phthalyl ethyl glycolate and butyl phthalyl butyl glycolate, sebacatcs such as dibutyl and dioctyl sebacates, adipates such as dioctyl adipate and di- (3,5,5-trimethylhexyl) adipate, glycol esters of higher fatty acids, organic phosphate esters such as tributoxyethyl phosphate, and the like. Choice of plasticizer is largely determined by the particular use. For non-propellant purposes the plasticizer should, of course, be inert, as for example in the production of lacquers, films and molded objects of various kinds. For propellant production the plasticizer may be active or inert. Combinations of plasticizer solvents can be employed to produce a plastic having the combined properties imparted by the individual plasticizers.

Any desired proportion of plasticizer solvent to nitrocellulose may be employed so long as sufficient is used to give the mixture a fluid, pourable consistency. In general, plasticizer solvent proportions insufiicient to produce a readily pourable slurry produce products which are excessively brittle. It is, of course, desirable not to use excessive amounts of plasticizer solvent, namely amounts which result in cured products that may be too soft. The amount of plasticizer solventemployed will vary to some extent 'accordingto the particular solvent used and the properties desired in the cured product. The specific proportions of any given casting solvent needed to produce the desired physical properties, such as hardness, can be readily determined by the skilled practitioner.

I have found that finely divided solids which are insoluble in the plasticizer can be incorporated into the nitrocellulose-plasticizer slurries-in considerable quantity without increasing viscosity of the slurry to the point where it is no longer pourable or requiring excessive proportions ofthe solvent carrier. The solids, furthermore,-are intimately and homogeneously dispersed both in the slurry and in the finished, cured composition. The dispersed solid may be any desired inert material such as a pigment or filler, e.g. zinc oxide, carbon black, talc, bentonite, mica, sericite, zinc sulfide, titanium dioxide, etc., or an oxidizing agent as will be discussed subsequently.

The nitrocellulose-plasticizer slurries are easily prepared by mixing the two components with suflicient agitation to produce a homogeneous mix. If a finely divided; insoluble solid is incorporated, it may be mixed with the nitrocellulose before addition of the plasticizer solvent or it may be added to the nitrocellulose-plasticizer slurry in which it is dispersed by agitation.

The slurries are fluid and normally pour rapidly. In some cases, the viscosity of the mix may be such that pouring rate is somewhat slow and for manufacturing expediency it may be desirable to accelerate pouring by the application of slight pressures. However, even the more vis cous slurries are sufficiently fluid to fill and conform to the shape of a mold or flow into an even film or coating without the application of heat or pressure. The slurries. may. be applied as coatings or films in any desired manner as by brushing, spraying or dipping. They can also be spread to form sheets of any desired thickness. To pro duce molded objects of any desired shape or size, the slurries are poured into a suitable mold.

Curing is accomplished by heating until the nitrocellulose completely dissolves in the casting solvent or plasticizer with consequent gelation and setting. Although the solution rate of nitrocellulose increases with increasing temperature, it is advisable to maintain temperatures which are well below the decomposition or auto-ignition temperature of the composition even though this involves somewhat longer curing periods. Curing temperatures generally used are in the neighborhood of about 50 to C. and to some extent are determined by the oomposition of the particular mix, namely such factors as the nitrogen content of the nitrocellulose, the type of plas ticizer and the properties of any added insoluble solids.- In any case, because of the small particle 'size of the nitrocellulose, curing is accomplished considerably faster than has hitherto generally been the case.

Since there is no appreciable sedimentation of the nitrocellulose during curing, the cured materials are uniform in composition throughout, possess excellent physical characteristics and are readily reproducible. Films or coatings may be made of any desired thickness and can be cured in a matter of minutes since curing is not accompanied by volatilization of a solvent. Since there is no loss of solvent or other dispersion media, there is no shrinkage; Objects of any shape or size are readily formed without requiring extrusion or molding under high temperatures and pressures. Curing temperatures can be maintained at a safe, low level. The fluid, pourable slu'rries not only are highly desirable for use in making films, coatings and molded plastic objects for a Wide variety of uses but they are also especially advantageous for impregnating paper, fabric, leather and the like.

My process is particularly suitable for use in making nitrocellulose propellant grains since it eliminates the dangers incurred by molding grains under heat andpressure and makes possible the formation of grains of any desired shape or size which are of uniform composition throughout, are cured more rapidly than has generally hitherto been possible at safe temperatures and are readily reproducible.

The nitrocellulose employed in making the propellant grains may be either the single-base type or the doublebase type containing a small proportion of nitroglycerine and the term nitrocellulose is to be so construed in the specification and claims. As aforementioned, the nitrocellulose should consist, predominantly by weight of 'particleswhich are not above about 10 mils in diameter. Smaller particles exhibit less tendency tosettle out and, therefore, prolong stability of the slurry. Preferablyme es maximum particle size I is about 100 microns -and,:for maximumshelf life, the maximum average particle diameter is about :50 microns.

.The casting solvent may be nitroglycerineor any'other high-boiling .organicisolveng. including plasticizers which are not auto-oxidant, but which possess the requisite casting properties of dissolving nitrocellulose slowly at ordinary temperaturesand rapidly at elevated temperatures to form asolid gel asafo'redescn'bed. The nitroglycerine casting solvent may be nitroglycerinealone or, as most usually employed -in the art, may contain 'a minorproportion of other good nitrocellulose solvents such as triacetin. The term nitroglycerine casting solvent is to be understood as referring to a-casting solvent con-- sisting predominantly-of nitroglycerine. As is common practice in the art, astabilizing agent such as diphenyl amine, should advisably be incorporated.

Anysuitable inert casting solvent such as theplasticizers enumerated above may be employed. Where such aninert solvent, namely a solvent which requires an external source of oxygen for'combustion, is used, it is advisable to'incorporate .an oxidizing agent into the propellant grains. Although inclusion of an-oxidizer is not essential in so far as the physical properties of the grain are concerned,-it increases the efficiency of the prm pellant by-providing for combustion of the casting solvent. The oxidizer is, preferably, in the form of a finely divided solid which is insoluble in the plasticizer. A'suflicient amount of the oxidizer may be incorporated to oxidize the casting solvent substantially completely without eliminating pourability of the slurry or requiring excessive proportions of the solvent carrier.

Any suitable,finely divided oxidizer, namelyany oxidizing agent which yields oxygen actively and readily, may be employed such as ammonium, sodium and potassium-perchlorates, ammonium, sodium, potassium and barium nitrates, and the like. For reasons'of stability, the inorganic oxidizersare preferable. However, organic oxidizers, such as hexanitroethane, mannitolhexanit-rate, cyclotrimethylene trinitramine and the like may also be used if satisfactorily desensitized.

Theinert casting solvent and oxidizer combination, being very much less sensitive than nitroglycerine, possesses the important advantage of greatly reducing processing hazards.

The nitrocellulose-casting solvent or nitrocellulose-casting solvent-oxidizer slurries are processed as aforedescribed, poured into-molds of the desired shape and size and cured by heating until the nitrocellulose dissolves'in the casting solvent. Since there is no sedimentation during curing, the grains are homogeneous throughout and can easily be reproduced'from slurries of similar composition. Because of the small particle size of the nitrocellulose, curing is rapid and complete sincethe plasticizer penetrates to the core of 'the small'pa-rticles without difliculty. The cured grains possess good physical and propulsive properties.

The following examples are illustrative of my invention, but, it will berunderstood, are in no way limiting.

EXAMPLE I 20 g. of triacetin and 5 g. of butyl phthalyl butyl glycolate were added to25 g. of nitrocellulose comprising,spherical particles of size predominantly within the range of about. 5-9 mils diameter (singlebase; 13.1 N), and A g. oflecithin. A homogeneous, fluidjs'lurry was formedwith'the aid of a mechanical stirrer. To this slurry was then added in portions with stirring, 48 g. of powdered potassium perchlorate. The resulting fluid mixture was deaerated by application of vacuum, poured into a suitable moldand cured for 2 days-at 70 C.

EXAMPLE [I '20 g. of .triacetin and 5 g. of tri-butoxyethyl phosphate were added with stirring to 25 g. ofnitrocellulose comprising spherical particles lof sizei predominantly by weight within therangeof about 5-9 mils diameter (single base, 13.1% N), andlA g, lecithin. To the=resulting slurry there was thenadded with stirring 46 g. offinely divided ammonium ps It?!)lot-ate. The resulting homogeneous fluid -mixture was deaeratedunder vacuum, poured into a suitable molduand cured-:forZ days at C.

EXAMPLE I III To asolutioncomprising 20 g.-of triacetin -and5g. of-diethyl phthalate were added 25 g. of nitrocellulose comprising spherical particles of size predominantly .by weight within the range of about 5-9 mils diameter (single base, 131% N), and g. lecithin. To the slurry termed by mechanical stirring there were; added, portionwise, 45g. of powdered ammonium nitrate. The homogeneous fiuid mixture was deaerated under vacuum, poured into;a suitable mold and cured for -2'days at 70 C.

EXAMPLE IV 15 g, of t-riacetin and 10 g. of methyl phthalyl ethyl glycolate were added with stirring to 25 g. of nitrocellulose comprising spherical particles of diameter about 5-9 mils (double base,:84% nitrocellulose, 12.9% N; 15% nitroglycerine; 1% diphenyl amine), and% g. of lecithin. 471g. of; powdered ammonium perchlorate were then added. The, resulting homogeneous fluid slurry was pouredinto amoldand was-cured at 70 C. for lweek.

EXAMPLE V 25 g. of nitrocellulose comprising spherical particles of diameterabo ut 5-9 mils (single-base, 13.1% N) were added to 25g. of a casting solvent comprising 72% nitroglycerine, 27% triacetin, 1% nitro diphenyl amine. The mixturewasagitated to'form a highly fluid slurry which was pouredinto a mold and cured for 5 days at 60 C.

EXAMPLE V1- 9.6 g. of triacetin, 14.4 g. of diethyl phthalate, 24 g. of nitrocellulose comprising spherical particles of diameter inthe range .of about 2 to,4 mils (single-base, 12.6%. N), 1 g. of lecithin and 84 g. of ammonium perchlorate were ,-mixed;with stirring and formed a fluid homogeneous slurry which was, poured intoa moldand cured for two days at 70-75 C.

EXAMPLE VII 12.5 g. of bis-(3,5,5-trimethylhexyl) adipate, 12.5 g. of diethyl phthalate,, 25 g. of nitrocellulose comprising spherical particles of ,d-iarneterin the range of about 2 to 3 mils (single-base, -12.6%'N)-, 1.25 g. of lecithin and 50;g.,of ammonium perchlorate were mixedwith stirring. Theresulting homogeneous, fluid slurry was poured into a mold and heated for two days at 7075 C.

EXAMPLE VIII 25 g. of dimethoxyethyl phthalate were added with stirring to-25 g. of nitrocellulose comprising spherical particles of diameter about 5 to 9 mils (single-base, 13.1% N),.and 1% g. of lecithin. 48 g. of ammonium nitrate were then added to the slurry. The homogeneous fluid mixture was deaerated under vacuum, poured into asuitable mold andcured for2 days at 70 C.

EXAMPLE IX 25 g. ofdiethylphthalate were added with stirring-to 25 g. of nitrocellulose comprising spherical particles of diameter about 5 to 9 mils (single-base, 13.1% N), and Mg. lecithin. 48g. of ammonium perchlorate were then added to the slurry. The homogeneous fluid mixture was deaerated under vacuum, poured into a suitable mold and cured for 2 days at 70 C.

The plastici-zed nitrocellulose products, preparation of which is summarized in Table I, were made according to the procedures described in the foregoing examples.

Table l Nltro- Particle Ratio, cellulose, size, Plastlcizer nitro- Remarks percent N microns cellulose: plastieizer 12.6 -15 Nitroglycerine/ 1:1 Cured 14 hrs.,

ethyl phthalatc, 1:1. Tough clear plastic.

10.5-11 5- 1-20 Dibutyl 1:1 Cured 15 min,

phthalate. 110 0.;

Clear flexible plastic.

13.4 2-50 Diethyl 1:1 Do. phthalate 1-20 Dibutyl 1:1 Do.

phthalate.

10.5-11.5- 1-3 Nitroglycerine/ 1:1 Cured 15 mln.,

diethyl 110 0.; phthalate, 1:1. Tough clear I plastic.

12.6 1-50 Nitroglycerinel 1:1. 5 Cured 14 hrs.,

diethyl 70 0.; phthalate, Clear flexible 80:20. plastic.

10.5-11.5--." 2-15 Dlbutyl 1:1 Cured 4 hrs.,

phthalate. 70 0.;

Siunfflezdble as re. 10.511.5 2-15 Nitrotglycerine/ 1:1 p Do. 6 y phthalate, 1:1.

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that the principles of this invention may be embodied in other forms but within the scope of the appended claims.

I claim:

1. A fluid, pourable, substantially homogeneous suspension of nitrocellulose in non-volatile plasticizcr solvent which dissolves the nitrocellulose readily only at temperatures of at least about 50 C., the nitrocellulose being in the form of substantially spherical particles, not larger than about mils in diameter, the plasticizer being present in amount sufficient to form a fluid, pourable slurry.

2. The composition of claim 1 in which the maximum 'diameter of the nitrocellulose particles is about 100 microns.

3. The composition of claim 1 in which the nitrocellu -lose particles have a maximum diameter of about 50 microns.

4. A process for making plasticized nitrocellulose compositions which comprises mixing nitrocellulose in the form of substantially spherical particles, not larger than "about 10 mils in diameter with sufficient non-volatile plasticizer solvent, which 1 dissolves the nitrocellulose readily only at temperatures of at least about 50 C., to form a fluid, pourable slurry, molding said fluid slurry and then heating the mixture to dissolve the nitrocellulose in the plasticizer.

5. The process of claim 4 in which the maximum diameter of the nitrocellulose particles is about 100 microns.

6. The process of claim 4 in which the nitrocellulose particles have a maximum diameter of about 50 microns.

7. A fluid, pourable, substantially homogeneous suspension of nitrocellulose and finely divided, inert solid in non-volatile plasticizer in which said finely-divided solid is insoluble and which dissolves the nitrocellulose readily only at temperatures of at least about 50 C., the nitrocellulose being in the form of substantially spherical particles, not larger than about 10 mils in diameter, the plasticizer being present in amount sufficient to form a fluid, pourable slurry.

8. The composition of claim 7 in which the nitrocellulose particles have a maximum diameter of about 100 microns.

grains I which comprises admixing nitrocellulose in the form of substantially spherical particles, not larger than about 10 mils in diameter, with anon-volatile casting solvent consisting essentially of nitroglycerine', said casting solvent being incorporated in sufflcient amount to form a pourable, fluid slurry, molding said fluid slurry and curing the molded nitrocellulose mixture by heating to a temperature at which said nitrocellulose dissolves in the nitroglycerine casting solvent and sets to form a solid propellant grain.

11. A process for making nitrocellulose propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose comprising particles not larger than about microns in diameter, with a non-volatile casting solvent which dissolves nitrocellulose readily only at temperatures of at least about 50 C. consisting essentially of nitroglycerine, said casting solvent being incorporated in suflicient amount to form a pourable fluid slurry, molding said fluid slurry and curing the molded nitrocellulose mixture by heating to a temperature at which said nitrocellulose dissolves in the nitroglycerine casting solvent and sets to form a solid propellant grain.

12. A process for making nitrocellulose propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose containing a minor proportion of nitroglycerine, and comprising particles not larger than about 10 mils in diameter, with a non-volatile casting solvent which dissolves nitrocellulose readily only at temperatures of at least about 50 C. consisting essentially of nitroglycerine, said .casting solvent being incorporated in suflicient amount to form a pourable fluid slurry, molding said fluid slurry and curing the molded nitrocellulose mixture by heating to a temperature at which said nitrocellulose dissolves in the nitroglycerine casting solvent and sets to form a solid propellant grain.

13. A process for making nitrocellulose propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose comprising particles not larger than about 10 mils in diameter, with a finely divided, oxidizer and non-volatile organic casting solvent in which said oxidizer is insoluble, said casting solvent being characterized by the ability to dissolve the nitrocellulose readily only at temperatures of at least about 50 C. and comprising a solvent which requires an external source of oxygen for combustion, said casting solvent being incorporated in suflicient amount to form a pourable fluid slurry, molding said fluid slurry and curing the molded nitrocel ulose mixture by heating to a temperature at which the nitrocellulose dissolves in the casting solvent and sets to form a solid propellant grain.

' 14. A process for making nitrocellulose propellant grains which comprises admixing nitrocelluose in the form of substantially spherical particles, said nitrocellulose containing a minor proportion ofnitroglycerine and comprising particles not larger than about 10 mils in diameter, with a finely divided, solid oxidizer and nonvolatile organic casting solvent in which said oxidizer is insoluble, said casting solvent being characterized by the ability to dissolve the nitrocellulose readily only at temperatures of at least about 50"v C. and comprising a solvent which requires an external source of oxygen for combustion, said casting solvent being incorporated in sufficient amount to form a pourable fluid slurry, mold ing said fluid slurry and curing the molded nitrocellulose mixture by heating to a temperature at which said nitrocellulose dissolves in the casting solvent and sets to form a solid propellant grain. j I

15. A process formaking nitrocellulose propellant grains which comprises admixing nitrocelluose in the form of substantially spherical particles, said nitrocellulose comprising particles not larger-than about 100 microns in diameter, with a finely divided, solid oxidizer and non-volatile casting solvent in which said oxidizer is insoluble, said casting solvent being characterized by the ability to dissolve the nitrocellulose readily only at temperatures of at least about 50 C. and comprising a solvent which requires an external source of oxygen for combustion, the casting solvent being incorporated in sutficient amount to form a pourable fluid slurry, molding the fluid slurry and curing the molded nitrocellulose mixture by heating to a temperature at which the nitrocellulose dissolves in the casting solvent and sets to form a solid propellant grain.

16. A process for making nitrocellulose propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose comprising particles having a maximum diameter of about 50 microns with finely divided, inorganic solid oxidizer and non-volatile organic casting solvent in which said oxidizer is insoluble, the casting solvent being characterized by the ability to dissolve the nitrocellulose readily only at temperatures of at least about 50 C. and comprising a solvent which requires an external source of oxygen for combustion, said casting solvent being incorporated in sufficient amount to form a pourable fluid slurry, the oxidizer serving to oxidize the inert casting solvent, molding the fluid slurry and curing the molded nitrocellulose mixture by heating to a temperature at which the nitrocellulose dissolves in the casting solvent and sets to form a solid propellant grain.

17. A process for making nitrocellulose propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose comprising particles not larger than about 10 mils in diameter, with a nitroglycerine casting solvent, said solvent consisting essentially of a major proportion of nitroglycerine and a minor proportion of triacetin, the casting solvent being incorporated in suflicient amount to form a pourable, fluid slurry, pouring the fluid slurry into a mold and curing the molded nitrocellulose mixture by heating to a temperature at which the nitrocellulose dissolves in the nitroglycerine casting solvent and sets to form a solid propellant grain.

18. A process for making nitrocellulose propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose comprising particles having a maximum diameter of about microns, with non-volatile casting solvent which dissolves nitrocellulose readily only at temperatures of at least about 50 C. consisting essentially of nitroglycerine, said casting solvent being incorporated in suflicient amount to form a pourable fluid slurry, molding the fluid slurry and curing the molded nitrocellulose mixture by heating to a temperature at which the nitrocellulose dissolves in the nitroglycerine casting solvent and sets to form a solid propellant grain.

19. A process for making propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose comprising particles not larger than about 10 mils in diameter, with finely divided ammonium perchlorate and nonvolatile casting solvent comprising a major proportion of diethyl phthalate, the casting solvent being incorporated in suflicient amount to form a pourable fluid slurry, pouring the fluid slurry into a suitable mold and curing the molded nitrocellulose mixture by heating to a temperature at which the nitrocellulose dissolves in the casting solvent and sets to form a solid propellant grain.

20. A process for making propellant grains which comprises admixing nitrocellulose in the form of substantially spherical particles, said nitrocellulose comprising particles not larger than about 10 mils in diameter, with finely divided ammonium nitrate and non-volatile casting solvent comprising a major proportion of dimethoxyethyl phthalate, the casting solvent being incorporated in sufficient amount to form a pourable fluid slurry, pouring the fluid slurry into a suitable mold and curing the molded nitrocellulose mixture by heating to a temperature at which the nitrocellulose dissolves in the casting solvent and sets to form a solid propellant grain.

References Cited in the file of this patent UNITED STATES PATENTS 2,417,090 Silk et al Mar. 11, 1941 

1. A FLUID, POURABLE, SUBSTANTIALLY HOMOGENEOUS SUSPENSION OF NITROCELLULOSE IN NON-VOLATILE PLASTICIZER SOLVENT WHICH DISSOLVES THE NITROCELLULOSE READILY ONLY AT TEMPERATURES OF AT LEAST ABOUT 50*C., THE NITROCELLULOSE BEING IN THE FORM OF SUBSTANTIALLY SPHERICAL PARTICLES, NOT LARGER THAN ABOUT 10 MILS IN DIAMETER, THE PLASTICIZER BEING PRESENT IN AMOUNT SUFFICIENT TO FORM A FLUID, POURABLE SLURRY. 